Dynamoelectric machine



y 5, 1953 T. w. MOORE 2,637,825

DYNAMOELECTRIC MACHINE Filed March 24, 1949 2 SHEETSSHEET l 1g 56 45 5 lig 27 14 41 6O 57 2O 1 55\ 6O INVENTOR ATTORNEYS May 5, 1953 T. w. MOOREDYNAMOELECTRIC MACHINE 2 SHEETS-SHEET 2 Filed March 24, 1949 mV 5 0 a 0Q m? w I} OM Wrrlli H wv TM. NJ MW 1. mm @W s 8 mv Q WV 3 RN 0? 3INVENTOR WW BY Waging ATTORNEYS Patented May 5, 1953 DYNAMOELECTRICMACHINE Thomas W. Moore, Dayton, Ohio, assignor, by mesne assignments,to American Machine & Foundry Company, New York, N. Y., a corporation ofNew Jersey Application March 24, 1949, Serial No. 83,260

18 Claims.

This invention relates to dynamoelectric machines and more particularlyto such machines employing permanent magnets.

The advantages of permanent magnets for the fields of dynamoelectricmachines are well understood, particularly with regard to freedom fromthe need for any exciter, the absence of windings, connections, sliprings, etc. However even with the use of magnetic alloys of highretentivity, it has been found difficult to develop sufficientmagneto-motive force without a relatively large and correspondinglyheavy magnetic structure, and because of the low tensile strength ofsuch alloys, even a low speed of rotation has been found to producecentrifugal forces sufficient to burst the magnet unless it isadequately reinforced or protected. In many cases the highly crystallinestructure of such magnet material and the shrinkage stresses resultingfrom its cooling combine to cause minor cracks within the magnet and asa result the tensile properties are uncertain and unreliable althoughthe compressive and magnetic characteristics are largely unimpaired.

It is also a characteristic of the high retentivity or high energyproduct alloy magnet materials that while th magnet may be magnetized toa high degree from an external source, if the low reluctance flux pathis interrupted even momentarily, the magnet will suffer a distinct lossof magnetism, which it cannot itself regain even though the lowreluctance path be subsequently restored. Thus when the magnet is placedin a magnetizing device, it may be magnetized to a high degree, butimmediately upon removal from the magnetizing device, and while it isbeing transferred to the stator in which it is to operate, thissubstantial loss of magnetization will occur, and when in place in thestator it will be found that its magnetism is substantially less than itwas upon its initial magnetization. On the other hand, if a, continuouslow reluctance path be maintained, the magnet will retain its highdegree of magnetization indefinitely, and thu provide for developing acorrespondingly higher voltage output.

It is the purpose of the present invention therefore to provide apermanent magnet rotor for a dynamoelectric machine which employs a highmagnetic retentivity alloy such as an ironnickel-aluminum alloy ofrelatively low inherent tensile strength which is received within alaminated structure or cage of high strength, such cage having magneticproperties on the portions opposite the poles of the magnet andnon-magnetic properties in the inter-pole areas, the overall structurebeing such that adequate strength is provided to allow the rotor to berotated at speeds greatly in excess of those at which the magnetic alloyitself would fail under centrifugal force. The invention also provides astructure which may be magnetized in a suitable fixture to a highdegree, and while the magnetizing force is still applied, keeper barsare inserted in areas provided between the poles and inwardly of theouter circumference to form a direct low reluctance path for by-passingthe flux from one pole to the other. The rotor with such keeper bars inplace is then withdrawnand may be placed in the stator in which it is tooperate. Once in position, the stator iron itself forms a low reluctancepath for the flux, and the keeper bars may then be removed. This makesit possible to magnetize the magnet to a high degree, and to retain highmagnetization throughout the placing of th rotor in the stator, andduring any subsequent removal of the rotor theerfrom which may benecessary during use of the machine, thus making possible asubstantially higher energy output from a given machine than could beobtained otherwise. Further, the magnetic characteristics are such thatit is only when the keeper bars are in place in the rotor that the rotorcan be freely withdrawn from the stator, the magnetic pull in theabsence of the keeper bars being such as to strongly retain the rotor inposition, and thus tending to avoid accidental withdrawal Withoutproperly placing the keeper bars in position.

It is accordingly one of the principal objects of the present inventionto provide a permanent magnet rotor for a dynamoelectric machine whichis easy and economical to manufacture, which has adequate strength towithstand the centrifugal forces effective thereon at high speeds, andwhich is of such structural characteristics as to be capable ofretaining a high degree of the magnetism during transfer from amagnetizing device to the stator of the dynamoelectric ma+ .chine andduring operation therein.

Another object of the invention is to, provide a simple and efiicientmethod of manufacturing a permanent magnet rotor which will maintain ahigh degree of permanent magnetism in the rotor as well as impartingadequate strength thereto for effective operation at high rotationalspeeds.

It is also an object of the invention to provide a dynamoelectricmachine wherein the stator includes removable parts which are adapted toserve as keeper bars for insertion in the axiar movement in the magnet.'bezforce fi-tted on shaft 28 or otherwise secured Fig. 1 is a view inlongitudinal section. of'ka. dynamoelectric machine constructedinaaccordance with the invention, the view being taken substantially onthe line l-! of Fig.2;=

Fig. 2 is a section on the'line2-2' of [Fig.1

showing two of the stator bolts mun'ted..in:'the;

casing and the other two stator bolts inserted in-therotor-and with thestator core and. winding shown. in elevation;

Fig.3 .is. an exploded perspective view of the .rotor of. Figs. 1 and 2;

Fig a is. a. somewhat diagrammatic sectional view illustrating the stepofbrasing together the componentparts ofithe rotor .jacketor cage;

Fig. 5 is afragmentary view in radial section showing the rotor. cagefollowing the brazing operation. of Figl;

Fig. "6 is- .a View similarto Fig. 5' showingfthe .rotoncagelfollowing.removal .of. the. bridging portions between adjacent pole extensions;and) .Fig. .7 is. asomewhat' diagrammatic. view illus- :tra'tingv theoperation.- or magnetizing the. .rotor in a magnetizing device.

Referring to the drawings, which illustrate a preferred embodimentofthepresent invention, Ithedynamoelectric machine is shown in Figs. '1and 2 as including .a laminated stator. core it of magnetic-materialprovided with the usual windings 'II. .The core I0 is. mounted in acasing whichincludesan annular shell portion 13' having inwardlyextending ribs M which engage. and

retain the core It to. leave air passages lt-extending lengthwise of thecasings'between these ribs. The casing shell. i3 is in turn mountedbetween end members l6 and I! which'are'held together by four elongatedbolts 20.

The rotor for. this machine includes a 'coreportion 2'5"'formed of.a'hig'h energy product (i. e. the product o'f'the remnant flux and. thecoercive force required to cancel the remnant (flux) magnetic alloy suchas an iron-nickel-aluminum alloy of the type commercially available forthis .purpose. Themagnet has spaced grooves or passages Zdwhich formrecesses extending axially along its outer surface to leave .a pluralityof salient pole portions 2?, four being shown. In order to secure thepermanent 'magnet'ZE' to the rotons'haftzfi,the magnet is shown .as caston atste'el sleeve .t'lllof'non-circular shape in section "to provide"a'secure' connection to the magnet.

As shown-"in :Figs; 1 .and" 2; the sleeve '3thasan "outline" in side-'elewation? which consists of: two

frusto cor'iica'lportionswith their, basestogether, :and the surface ofthesleevehas angularly spaced; axially extending grooves 3 l into whichzthe'. magnetic material of magnet 25 is cast. These: grooves thuscooperate with the material .ca'sts' thereint'o prevent relativerotation of the sleeve and magnet, and the frusto-cohical configurationof the sleeve similarly" looks it against Sleeve "39 may suitablemagnetic material such =.as steel.

thereto, as :by the pin 32 indicated in Fig. 1, and the shaft is in turnmounted in the stator in any suitable way, as by the means of thebearing 33 and integral web portion 35 of the end member l6 of thestator casing.

Rotor magnet 25 is provided with an annular jacket-norcage-whichincludes laminations of a These laminations are formed toprovide pole eXten sions opposite and in alignment with the respectivepoles 21 of the magnet. The sectors between the. pole extensions ii! arefilled in with preformed. nonemagnetic bars M of chromium bearingv.oopperor. the like. have .aictensile strength comparable with that ofThese bars M may the steel-. portions40 and also have high electricalconductivity and thus function as a short cir- "cuited turnaround thepole face, tending to maintain-uniform flux through the pole face.

The pole extensions-M each include side portions 42 which extendinwardlyto fit withintthe groovesZBlin magnet25, 'and'bars' ll have beveled'inner'surfaces 43 which are'secured to the side portions of thepole'extensi'ons, the outersurface M of each'bar tl being cylindrieallycurved .to complete" tthe' cylindrical outer surface of the rotor.The'rotorcage also includes en'drings ofchromium'bearing coppenand theseringsare drilled'as shown at '46 andtlie pole. extensions 40 arecorrespondingly drilled and slotted. asshown at 4T. .tore'ceive thecopperv amortissenr bars '48 "which form a short circuited windingacrosslthe face .ofthe rotor. The design of; the pole facemayadvantageouslybe suchithat. maximum. cross sectional area is allottedtoth'e distributed'winding 41; This alsoinvolveshighly saturatingthemagnetic sections between the conductors comprising the squirrel cagewinding, the saturation ofsuch sectionsprovidingadditional stability tothe waveform and further reducing the effects 'laminations of which thec'ageisicomposed are 'initiallyin annular 'form and include all the poleextensions, the side portions 42 of adjacent pole extensions, beingconnectedby integralbridging 'portions'50, and it will also'be notedthat the inner edges of the-laminations have cylindrically curved seatsor recesses5l therein adjacent each bridging portion and reducing thewidth thereof. 'In forming the cage;these'laminations are assembled in;astack as'shown in'Fig. 4 with thebars 4 l the: end rings 45 and theamortisseur Ibars48'in a brazing fixture comprisingacylindricalshelliifi and top. andbottom plates 56 and 5.1. Theupper edge. of shell'55 isbeveledoutwardly to provide withv the. top plate 56 .a funnel-likeannular opening into which a suitable brazing compoundzmay be poured tosecure all of these parts: :of..-.thev :c'age: together.

Flt/Will; be. :seen that; the brazing: talics: place alongwan:inclinedplane such that *the brazed joint is subjectedllargely to' shear, thearea in shear b'eing thusrsufiiciently great-to be comparable instrengthwith the area of the polepieces inwardly ofthe-crossbars it. Thisconstruction t'ends' t'o maintain a consistent stress" condition: inthecage and avoids local stress "concentrations.

Atthesame-time thecontoursof the pole face'are such as to reduceundesirable interpole stator :leakage, and since theimagneticz'pole-faces donut terminate abruptly, facilitate the development of adesirable wave form.

Fig. 5 shows the appearance of the cage following this brazingoperation, with the bars 4| secured to the side portions 42 of the poleextensions but with the bridging portions 50 still intact, and theassembly is then heat treated to develop the maximum strength in thecopper alloy parts. The bridging portions 50 are then milled or groundaway to provide air gaps 60 between the side portions 42 of adjacentpole extensions 4D, and also any excess brazing material on the innersurface of the cage is removed. Fig. 6 shows the appearance of the cageafter these operations, and it will be noted that adjacent poleextensions 40 are entirely separate from each other magnetically and aremaintained with their adjacent side edges in spaced relation across thegaps 60 by means of the non-magnetic bars 4|. The cage is then mountedon magnet 25 in proper relation thereto, with the side portions 42 ofthe pole extension being received in the outer portions of the grooves26 in the magnet. The cage may be readily secured to the magnet by beingheated and shrunk thereon, and the completed structure is turned tofinished dimensions before being magnetized and mounted in the stator.

Fig. 7 illustrates the operation of magnetizing the rotor in amagnetizing device 65, which is shown as an annular frame 65 having fourradi- 1 ally arranged salient poles 61 mounted therein and provided withwindings B8 and wooden spacer blocks 69. To magnetize the rotor, it isinserted in the device 65 as shown in Fig. 7, and current is applied tothe magnetizing device. Preferably the poles 61 of the magnetizingdevice are placed in direct contact with the pole extensions 40 of therotor to provide a minimum reluctance path during the magnetizingoperation.

If the rotor is simply removed from the magnetizing device, as isnecessary in transferring it to its working position in the stator, itsuifers a marked and quite substantial decrease in its degree ofmagnetization. Assuming, by way of example, a magnetic material whichcan be magnetized to a peak condition of the order of 80,000 lines persquare inch following the complete removal of the rotor from themagnetizin device in the absence of the maintenance of a low reluctancepath for the flux, the magnet may lose as much as 50 per cent of itsmagnetism, so that when reinserted in the stator, it is magnetized onlyto a level of about 40,000 lines per square inch. Even though the statorthen forms a relatively low reluctance path, regain any magnetism Whichis lost during its period of transfer when there was no complete lowreluctance flux path, however short that period may have been.

In accordance with the present invention, however, a low reluctance pathis established for the flux prior to withdrawal of the rotor from themagnetizing fixture, and while there may be some loss of magnetismbecause of saturation in this flux-by-pass circuit, the magnet retains amuch higher level of flux density than when it is simply removed from amagnetizing device without providing such a by-pass circuit.

When the rotor is then placed in the stator, this by-pass circuit isdiscontinued, and the flux traverses the air gap between the rotor andthe stator and the magnetic circuit of the stator. The presence of theair ga interposes a short high reluctance path for the flux which,however, is necessary for the operation of the mathe magnet does notchine, and while it results in some loss of permanent magnetism, a fluxdensity is nevertheless retained which is still substantially above thatwhich would result from the direct transfer of the rotor from themagnetizing device in the absence of the by-pass circuit. For example amagnetism of the order of 75,000 to 78,000 lines per square inch hasbeen successfully maintained, representing a substantial increase abovethe 40,000 lines per square inch density obtainable in the absence ofthe use of the by-pass circuit.

This result is accomplished by temporarily inserting removable keeperbars of magnetic material in the grooves 26 between the side portions 42of adjacent pole extensions 40 to form a flux by-pass between adjacentpole extensions, and a simple and eifective form of keeper bar isprovided by the steel stator bolts 20. Thus as shown in Fig. 1, thestator casing is so designed that the bolts 20 are somewhat longer thanthe rotor, and also the diameter of these bolts is correlated with thedimensions of the rotor to provide for free insertion of the bolts inthe grooves 26 in contact with the side portions 42 of the poleextension which extend into each of these grooves. Satisfactory resultsfrom this standpoint have been obtained from the notches 5| in the cagecurved about a radiu slightly larger than that of the bolts, for examplea radius of ,4 inch when the bolts 20 are 1% inch in diameter, toprovide working clearance while assuring adequate areas of contactbetween the bolts and the walls of recesses 5|.

With this construction, the bolts 20 are inserted in grooves 26following the magnetizing operation and before the rotor is removed fromthe magnetizing device. Thereafter during transfer of the rotor to thestator, the bolts will be magnetically held in contact with the curvedrecesses 5| of the side portions of adjacent pole extensions to form aflux by-pass therebetween, but after the rotor has been mounted in thestator, the magnetic flux will also flow through the stator, and thebolts can be readily removed and mounted in proper position to hold thestator casing together. This stage in the assembly of the machine isillustrated in Fig. 2, which shows two of the bolts already in thecasing while the remaining two bolts are still inserted in the rotor.

In this way the removal of the rotor from the stator is rendered simpleand easy, avoiding the necessity to exert the substantial force whichwould be otherwise required to pull the rotor out.

In the operation of this dynamoelectric machine, the rotor cage servesas an effective reinforcing means for the permanent magnet 25, which isrelatively brittle and incapable when unsupported of withstanding thecentrifugal forces effective thereon at high speeds, and it is thuspracticable to operate the machine efficiently at high speeds, forexample within a range up to speeds of the order of 12,000 to 15,000 R.P. M. The bars 4! are of high tensile strength and thus add substantialmechanical strength to the cage as well as supplementing the shortcircuiting effect of the amortisseur bars 41, and the end rings 45 alsoadd strength to the cage and thus to the rotor as a whole. In addition,the construction of the rotor as described which provides for the use ofremovable keeper bars is particularly advantageous in maintaining themaximum degree of permanent magnetism in the rotor for efiicientoperation, and this result is facilitated by the design; of the machineas a whole which makes available the stator bolts "for use as the keeperbars duri ng assembly or disa'ssemhly of :themachine. It -wili'ialso beseen "that these practical advantages are obtained in a constructionwhich is relatively easy and econominal to producegrequiring only simplefabricating operations.

The invention I also provides for avoiding the objectionabledemagnetizing eit'ects' resulting from'transient load currents'i'n thestatorwindmg, further assuring th'e maintaining t a 'h-igh levelof'magnetization inthe permanent magnet. The effect of asubstantial-transientcurrent in the stator is to create a-counte'rmagnetomotive iforce which opposes the permanent magnetism withe -rotor,and maybe considered asha'ving an :efiect similar to increase in: thereluctance of the path; The effect of'thisidemagnetizing'force may bellessened' by-the provision-of the limited air -gaps:tic-between adjacentarms-M of the poie .extcnsionsr eachgap fidbeing-of such length andarea as shown that it maintains the magnetic circuits of adjacent polesseparate and i does. not iresultz'iin any substantial. leakage duringnormal operation of the machine'but doesprovidea leakiageipath' 'fort'hepassage of aportion' of the flux :wh'en there-"is a strong or abnormal'counter- -magnetomotive==forceysuch as the conditions describe'drabove.Thisi -luxleakage paththus serves tt'o' zmai'ntain "the totalrflux'throughtlie permanentmagn'et at; a relativelyhigh level,- notwith-'-standing' the' presence of a-Phigh 1 counter-nunin the stator: Thesize of the air gapsfiil' may be selected as desired to produce desiredoperating ch'aracte'ristics.

'ViZ-hilethe method'andform of-apparatus-hereinv'described. constitutepreferredembodiments of thcmi-nvention, it is to be understood that theinventionnis not: limited tothis precise method and-form of apparatus,andthat changesmay bejma-de therein without departing from thescope-ofthe inventionwhich is defined in the appended claims.

that is claimed is:

1; A:rotor adaptedr'for use in a 'dynamoelectric machine: having astator comprising a- -p'erman'ent magnet, poleextensions of magneticmaterial in contact with thepoles of said magnet, means maintaining saidpole-extensions in circumferentially spaced relation with each other'toform gapsdefinin'g paths of substantially-higher reluctance thanathereluctance of" theair gap be tween said rotor and the stator in saidmachine, means defining air gaps extending axially through said rotorwithin the outer circumference thereof and radially inwardly of saidhigh reluctance paths in continuous relationwith" the ends of adjacentsaid pole extensions, and keeper bars-of magnetic material adapted toberem'ovably recei'ved in said'air gaps in flux Icy-passing relationwith adjacent said pole extensions to complete the magnetic circuitwithin said rotor.

2 A rotor adapted for use' in adynamoelectric machine having a statorcomprising a permanent magnet, pole extensions of magnetic" material incontact'with the poles of said magnet means maintaining said poleextensions in circumferentially' spaced relation with each otherto-"fo'rm paths between'each other of substantially-higher reluctancethan the reluctance of the air gap between. said rotor and the stator insaid machine, said paths extending axially through said rotor within theouter circumference thereof, the adjacent faces of said pole extensionsbeing shaped t'o form recesses extending axially th-roughsaidrotoriwithin the outer circumf erence' thereof,

and 'k eeper bars (if-magnetic material-adapted to be removably received-in-'-said'-recesses inlflux 'by-passing relation with "adj acen't' saidpole extensions to ccmplete th'e magnetic cir'cuitwithi'n said' roton=3'i A rotor adapted for-use in a dynamoelectric --machine having astator, comprising a permanent magnet having salient'poles, acircumferentially continuous cage surrounding said magnet and includingpole extensions of magnetic material secured to said magnet incircumfertendi ng grooves in the surface thereof between adjacent po1esalients and radially inwardly of said-cage; said pole extensionsprojecting partially inwardlyof said grooves and cooperating therewithto receive keeper bars of magnetic inate'ria'l in flux by-gpassingrelation with said adjacent edges of said'pole extensions for completingthe magnetic circuit within said rotor 'to pre'vent lossof magnetismwhen said rotor is not said stator:

a A rotor adapted for use in a dynamoelectric machine having a statorcomprising a permanentm'agnet, pole extensions of magnetic mate rialsecure'dto said magnet incircumferentially spaced relation to form gapsof substantially higher reluctance than the reluctance of the air'gapb'etweensaid rotor and the; stator in said machine, saidpoleextensions'having inwardly inclined-portions on the outer surfacesthereof adjacentthe side edges there-oi, complementarilyshaped bars ofnon-magnetic material secured-to saidfinclinedportions of adjacent poleextensions and extendingaxially of said rotor to-m aintain adjacent saidpole" extensions in said spaced-relation, said magnet having.axiallyarrangedflpassagesin'the surface thereof underlying-thespaces'between adjacent edges of said pole extensions forreceivingkeeper bars of magnetic material to form ,a flux by-passbetween adjacent said pole extensions for completing the magnetic;circuit within said rotor.

51A rotor for a'd'ynamoelectric machine com prising a permanentmagnetcore of highenergy product havi ng a plurality of salient poleswith recesses therebetween, a cage completely surrounding-the peripheryof said cor'e in the form of-lamina'tions of high strength magneticmateri-aloverlying each of thepole salients and forming pole extensionstherewith, adjacent pairs of said pole-extensions having portionsinclined-inwardlyand-projecting toward each other in circumferentiallyspaced relation to leave an air gap therebetween, and preformed solidbars I of non niagnetic material bonded to the sides of said poleextensions in radially overlying relati'on'with said air gaps to form acomplete uniform circumference for said cage developing high strengththroughout the periphery thereof, saidbars' having inclined surfacescomplemene tary to and bonded directly to said inclined portionsof'saidpole extensions to provide bonded areas subject to shear forces intheoperatlon of said'rotor and with said'bonded areas being ofsubstantial size providing strength therein comparable'withsaid poleextensions to maintain a consistent stress condition in said cageavoiding local i stress concentrations.

' 6.:-A. rotor adaptedfor use in-a dynainoelectric machine having-astator comprising a permaassisted nent magnet, an annular cage mountedon said magnet and formed of alternate non-magnetic portions andmagnetic portions forming pole extensions, said rotor having air gaps ofsubstantial angular extent extending axially therethrough betweenadjacent said pole extensions and radially inwardly of said non-magneticportions to form paths of substantially higher reluctance than thereluctance of the air gap between said rotor and the stator in saidmachine and keeper bars of magnetic material adapted to be removablyreceived in said air gaps in flux bypassing relation with adjacent saidpole extensions to complete the magnetic circuit within said rotor inthe absence of an external magnetic circuit therefor.

7. A rotor for a dynamoelectric machine comprising a permanent magnetcore of high energy product and having a, plurality of salient poleswith recesses therebetween, a cage completely surrounding the peripheryof said core in the form of laminations of high strength magneticmaterial overlying each of said salient poles'and forming poleextensions therewith, said pole extensions having portions inclinedinwardly and projecting toward each other at a relatively shallow anglewith respect to each other and in circumferentially spaced relation toleave an air gap therebetween, bars of non-magnetic material bonded tothe outer surfaces of said inclined portions of said pole extensionsover a substantial area thereof and having outer surfaces in thecircumference of said pole extensions, and keeper bars of magneticmaterial adapted to be removably received in said air gaps in fluxbypassing relation with adjacent said pole extensions to complete themagnetic circuit within said rotor.

8. A dynamoelectric machine of the character described comprising astator having a winding, a rotor mounted for rotation within said statorand including a permanent magnet, pole extensions of 'magnetic materialsecured to said magnet in circumferentially spaced relation, the sideedges of said pole extensions and said magnet having cooperatingportions forming air gaps extending axially through said rotor betweeneach adjacent pair of poles and forming paths of substantially higherreluctance than the reluctance of the air gap between said rotor andsaid stator, end members for said stator, and bars of magnetic materialfor connecting said end members together, each said bar being of suchdimensions as to be received in one of said air gaps in contact withadjacent said pole extensions to form a fiux by-pass therebetween forcompleting the magnetic circuit within said rotor independently of saidstator.

9. A dynamoelectric machine of the character described comprising astator having a winding, a rotor mounted for rotation within said statorand including a permanent magnet, pole extensions of magnetic materialsecured to said magnet in circumferentially spaced relation, the sideedges of adjacent said pole extensions having surfaces circumferentiallycurved about the same axis, end members for said stator, and cylindricalbars of magnetic material for connecting said end members together, eachsaid bar being removably receivable in the space defined by said curvedsurface portions and in contact with each thereof to form a flux by-passbetween adjacent said pole extensions for completing and maintaining themagnetic circuit internally of said 10 rotor in the absence of anexternal magnetic circuit therefor.

10. A dynamoelectric machine of the character described comprising astator having a winding, a rotor mounted for rotation within said statorand including a permanent magnet and an annular cage mounted on saidmagnet and formed of alternate nonmagnetic portions and magneticportions forming pole extensions magnetically separated from each otherby air gaps, end casing members for said stator, and bars of magneticmaterial for connecting said end members together, each said bar beingof such dimensions as to be received in one of said air gaps in contactwith adjacent said pole extensions to form a flux by-passtherebetweenfor completing the magnetic circuit withinv said rotorindependently of said stator.

11. In a method of manufacturing a rotor for use in a dynamoelectricmachine having a stator, the steps of securing pole extensions ofmagnetic material to a permanent magnet having a high magneticretentivity during the continuance of a low reluctance magnetic path andhaving substantially reduced retentivity upon the interruption of suchpath with adjacent edges of said pole extensions in circumferentiallyspaced relation to provide air gaps therebetween, magnetizing theresulting structure in a magnetizing device, then inserting keeper barsof magnetic material between adjacent said pole extensions in fluxby-passing relation therewith while said rotor is in said magneticdevice to complete the magnetic circuit within said rotor, and removingsaid rotor from said magnetic device with said keeper bars in place.

12. In a method of manufacturing a rotor for use in a dynamoelectricmachine having a stator, the steps of securing pole extensions ofmagnetic material to a permanent magnet having a high magneticretentivity during the continuance of a low reluctance magnetic path andhaving substantially reduced retentivity upon the interruption of suchpath with adjacent edges of said pole extensions in circumferentiallyspaced relation to provide air gaps therebetween, magnetizing theresulting structure in a magnetizing device, then inserting keeper barsof magnetic material in the air gaps between adjacent said poleextensions in flux by-passing relation therewith while said rotor is insaid magnetic device to complete the magnetic circuit within said rotor,transferring said rotor from said magnetic device to said stator withsaid keeper bars in place, and thereafter removing said keeper bars.

13. In a method of manufacturing a rotor for use in a dynamoelectricmachine having a stator, the steps of forming a plurality of individualannular laminations of magnetic material each including a plurality ofpole extensions connected by integral bridging portions each locatedradially inwardly of the outer circumference of said pole extensions,securing a plurality of said laminations together in stacked relationwith said bridging portions forming axially arranged indentations in thecircumference of said stack, bonding axially extending bars ofnon-magnetic material to adjacent said pole extensions within saidindentations in overlying relation with said bridging portions, removingsaid bridging portions to leave said pole extensions connected in spacedrelation by said bars, and assembling said stacked laminations upon apermanent magnet having salient holes with said bridging portionslocated in the spaces between said holes.

aesmses 1-1 1%. In a method of manufacturing a rotor for use in ady'narhoelectfic machine h'avirigi a'stator; the steps of forming anannular cageof rria'grietio material havin ahigh" rhag'iiet'ic'rethti-vity during the continuance of a" low reluctancefrhagnetic pathand having substantially reduced--retentiv=" ity upon the interruptionof such path coinpris-' ing a plurality of pole extensions connected bybridging portions located radially: inwardly ,o ftlie outercircumference of said, pole extensions to form axially extendingindentations mime ci'r cumference of said cage, bonding axisuyaenenamgbars of nonma netic material to, adjacent said pole extensions" of saidcage vvithi' said 'in-' dentations in' overlying" relation viithisaidhridging portions, fernov-inglsaid bfidgir g portions to leavead'jacentedg'es of Sa'id'pQIe extensjionsin circumferentia'lly spacedreiatidnprormin ail: gaps of relatively high reluctance; mountin saidcage on a permanent magnet, magnetizing the 15. The method orremoving'aermennt mag net rotor having internal pas's'ages betweeri ad'jacent polepieces from it s'operative'pos'itio'ri inthe stator of a dynamoelectricnia'chineghaving a" casling and end shell member" bolted thereto whichcomprises the'steps of removing the" bolts ,froni said end shell andremoving thesame; ""e'rtin'g' the vbolts in said passages in fiuii'bypassing-relation therewith to establish arriaghtifc .0 'ciiit.eritir'e'ly within the rotor, and thereafter W thdraw ing the rotorfrom said stator' with said h'olt's' in position'insaid passages. v

16. The method of removing a ermanem'mae net rotor havinginternalrpassaees'betvveen'adlfacent pole pieces from the'statoi of adyriam'o'e'lejc tric'machine having a casing and' erid ShBILIfiBI fihers bolted thereto which omprise the'hs'teps ofremoving the bolts fromsaideii'd'srien; withdrawing the end shell from one endofxsaidicasing,irisertin said bolts into saidpassa'geslinthero" i between adjacent polepieces" andjin Ina 116 a contact therewithforestablishing al'oiivlrlfi ae' flux path ent rely Withiii' the .pe "by of "aid rotor and withouttravel offa siib slope f the flux into the stator; said bolts.einjg-heldifi said passages under the force of magnate attraction andproviding for Withdravv' from said stator substantially free or,inag'ne'tic attraction therebetween, and thereafter with- =.of Saidrater 12-- drawing said rotor frornsaid stator withsaid bfo'lts inaidpassages.

1"1. Themjethod ortremovin 'aperinanenfinisgne't rotor" having internalpassagesbetvveeiadj 1 ce'rit pairs 0f pole pieces from the stator vo'famrnamoelectric machine which @compris'eslthe steps of removing theends-hell from the dynamoel'ecf tricimachihe, inserting magnetickeeperbars in said passages within said rotor to establish a low reluctancemagnetic path entirely within said rotor said keeper bar's being inmagnetic contact with adjacent pole pieces and being. held-thereinbymagneticattraction While substantiallyreducingltheflux'traversinglsaid stator,randlthereafter" Withdrawingvsaid ro'tor"from said statorwithis'aid keeper barsin place therein,

18. ,In a dynamoelectric machine of the charac terldesoribed having acasing including a pair; .o-f

opposite end members, the cornbinatiton; sofa stator h'aving a Winding,throughbolts iof mag netic material for removably securing said-endplates together with said stator' within said casing', a rotor mountedfor rotation Withinsaidsta-e tor and including a permanent magnet,pole-en tensions of magnetic material secured to saidmagnet incircumferentially .spacedrrelation said magnet and the side edgesof saidpole extensions havin "cooperating portions forming axially :ar

ranged air gaps through said rotor between each adjacent pair of poles,and eachsaid gap-being proportioned to receive one of said throughhol-tsin .oontact with adjacent-said pole extensions to form a flux by-passtherebetween for completing thelmagnetic circuit ithin said rotorindependently of said stator during removal ofsaid 'rotor from saidstator or replacement thereofwithin saidstator. H I

THOMAS W. MOORE.

References Cited in the file of this patent UNITED ,STATES'PATENTS'Number Name Date 1,195,861- Smith Aug-.22 r9136 moon-59' Kuhn-Frei Julya 1923 meaere Blake Feb; 28, 1924 13957580 Barlow 'Mayj1jl934'139'9-11046- Bohli Feb; 12], 1 933 $024,745; Rey-riders- 'Dec1 117;, 1935 2-;oea4 1e Cotterman Apr.'21j,"-1 936- 2,078,805 Merrm p-1- 2"], r9372153563 Hjiibacker Apr. 1 '1";"1*9 39' a er'pee "Huha'cker Jan-1 o,rero- 2,'255-,477 Tognola Sept. 9', 2,279,846 $tap1eton Apr. 314; 19422,35 4 ,55 Saw-yer July 25,1944 2147 647 Goodwin Augl'24, 1948"

